In order to effectively utilize a hybrid vehicle, an attempt to utilize the hybrid vehicle as a power supply facility has conventionally been made. As such a hybrid vehicle, a hybrid vehicle including a dedicated inverter for converting a DC (Direct Current) voltage generated in the hybrid vehicle to AC 100V has been known.
Meanwhile, Japanese Patent Laying-Open No. 04-295202 discloses an electric motor drive and power processing apparatus capable of generating an AC voltage and supplying the voltage to an external device without including a dedicated inverter. The electric motor drive and power processing apparatus includes a secondary battery, inverters IA, IB, three-phase AC motors MA, MB, and a control unit. Three-phase AC motors MA, MB include Y-connected three-phase windings CA, CB respectively, and an input/output port is connected to a neutral point NA of three-phase winding CA and a neutral point NB of three-phase winding CB through an EMI filter.
Inverters IA, IB are provided corresponding to three-phase AC motors MA, MB respectively, and connected to three-phase windings CA, CB respectively. Inverters IA, IB are connected to the secondary battery in parallel.
In the electric motor drive and power processing apparatus, inverters IA, IB can generate AC power of which sine wave is regulated across neutral points NA, NB and can output the generated AC power to the external device connected to the input/output port.
Generally, while the three-phase AC motor including a Y-connected three-phase coil as a stator coil is revolving, a harmonic of order of multiple of 3, of counter-electromotive force generated in the coil of each phase appears in a potential of the neutral point of the three-phase coil. Briefly speaking, assuming that the number of revolutions of the three-phase AC motor is denoted as ω, induced voltage eu, ev, ew of the coil of each phase is expressed in the following equation.
                              e          U                =                                            e              1                        ⁢            sin            ⁢                                                  ⁢            ω            ⁢                                                  ⁢            t                    +                                    e              3                        ⁢            sin            ⁢                                                  ⁢            3            ⁢                                                  ⁢            ω            ⁢                                                  ⁢            t                    +                                    e              5                        ⁢            sin            ⁢                                                  ⁢            5            ⁢                                                  ⁢            ω            ⁢                                                  ⁢            t                    +          …                                    (        1        )                                          e          V                =                                            e              1                        ⁢                          sin              ⁡                              (                                                      ω                    ⁢                                                                                  ⁢                    t                                    -                                                                          ⁢                                                            2                      3                                        ⁢                    π                                                  )                                              +                                    e              3                        ⁢            sin            ⁢                                                  ⁢            3            ⁢                          (                                                ω                  ⁢                                                                          ⁢                  t                                -                                                                  ⁢                                                      2                    3                                    ⁢                  π                                            )                                +                                    e              5                        ⁢            sin            ⁢                                                  ⁢            5            ⁢                          (                                                ω                  ⁢                                                                          ⁢                  t                                -                                                                  ⁢                                                      2                    3                                    ⁢                  π                                            )                                +          …                                    (        2        )                                          e          W                =                                            e              1                        ⁢                          sin              ⁡                              (                                                      ω                    ⁢                                                                                  ⁢                    t                                    -                                                                          ⁢                                                            4                      3                                        ⁢                    π                                                  )                                              +                                    e              3                        ⁢            sin            ⁢                                                  ⁢            3            ⁢                          (                                                ω                  ⁢                                                                          ⁢                  t                                -                                                                  ⁢                                                      4                    3                                    ⁢                  π                                            )                                +                                    e              5                        ⁢            sin            ⁢                                                  ⁢            5            ⁢                          (                                                ω                  ⁢                                                                          ⁢                  t                                -                                                                  ⁢                                                      4                    3                                    ⁢                  π                                            )                                +          …                                    (        3        )            
Here, e1, e3, e5 . . . are constants specific to each motor. Based on Equations (1) to (3), a potential of neutral point eN is expressed in the following equation.
                                                                        e                N                            =                                                1                  3                                ⁢                                  (                                                            e                      U                                        +                                          e                      V                                        +                                          e                      W                                                        )                                                                                                        =                                                                    e                    3                                    ⁢                  sin                  ⁢                                                                          ⁢                  3                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                                                      e                    6                                    ⁢                  sin                  ⁢                                                                          ⁢                  6                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                                                      e                    9                                    ⁢                  sin                  ⁢                                                                          ⁢                  9                  ⁢                                                                          ⁢                  ω                  ⁢                                                                          ⁢                  t                                +                …                                                                        (        4        )            
Here, e3, e6, e9 . . . are constants specific to each motor. As shown in Equation (4), potential of neutral point eN includes the harmonic of order of multiple of 3, of counter-electromotive force. Therefore, if three-phase AC motors MA, MB revolve while the AC power is generated across neutral points NA, NB in the electric motor drive and power processing apparatus disclosed in Japanese Patent Laying-Open No. 04-295202, the harmonic as above is contained as disturbance in the generated AC power. Japanese Patent Laying-Open No. 04-295202, however, does not address such a problem in particular.